1. Field of the Invention
This invention relates to electrical switching apparatus and, more particularly, to circuit breakers having two or more pairs of separable contacts.
2. Background Information
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which heats and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system.
U.S. Pat. No. 5,541,561 discloses an integral electrical circuit controller apparatus including an electrical contactor having contacts, a circuit breaker having separable contacts connected in series with the electrical contactor, a trip mechanism responsive to current flowing through the separable contacts for tripping the contacts open in response to predetermined current conditions, and a current throttle impedance for limiting short circuit current.
U.S. Pat. Nos. 5,301,083 and 5,373,411 describe a remotely operated circuit breaker, which introduces a second pair of contacts in series with the main separable contacts. The main contacts still interrupt overcurrent, while the secondary contacts perform discretionary switching operations.
There exists the need to improve the operating voltage and/or interrupting capacity of circuit breakers without corresponding significant increases in cost of capital expenditures, development cycle times, and circuit breaker cost and size (e.g., width).
There is room for improvement in circuit breakers.
The present invention is directed to a circuit breaker including first and second circuit breaker mechanisms, an operating handle having on and off positions, and first and second links from the operating handle to the respective first and second operating mechanisms. The two circuit breaker mechanisms include two operating mechanisms, two trip mechanisms and two sets of separable contacts in series between line and load terminals. The links engage the operating mechanisms to move the first and second separable contacts between corresponding closed and open positions thereof responsive to the on and off positions, respectively, of the operating handle.
According to the invention, a circuit breaker comprises: a housing; line and load terminals; a first circuit breaker mechanism comprising: a first set of separable contacts, a first operating mechanism for moving the first set of separable contacts between an open position and a closed position, and a first trip mechanism cooperating with the first operating mechanism for moving the first set of separable contacts from the closed position to the open position thereof; a second circuit breaker mechanism comprising: a second set of separable contacts in series with the first set of separable contacts between the line and load terminals, a second operating mechanism for moving the second set of separable contacts between an open position and a closed position, and a second trip mechanism cooperating with the second operating mechanism for moving the second set of separable contacts from the closed position to the open position thereof; an operating handle having an on position and an off position; a first link from the operating handle to the first operating mechanism; and a second link from the operating handle to the second operating mechanism, wherein the first and second links engage the first and second operating mechanisms to move the first and second sets of separable contacts, respectively, between the corresponding closed and open positions thereof responsive to the on and off positions, respectively, of the operating handle.
Preferably, the second trip mechanism includes a bimetal element in order to provide a thermal trip function.
The second set of separable contacts may include a fixed contact and a movable contact, with the bimetal element being electrically interconnected with the movable contact. The bimetal element may have an input electrically interconnected with the movable contact of the second set of separable contacts and an output, which is electrically interconnected with the load terminal.
The first and second trip mechanisms may include a magnetic trip coil in order to provide an instantaneous magnetic trip function. The first and second sets of separable contacts may include a fixed contact and a movable contact, the magnetic trip coil of the first trip mechanism may be electrically interconnected between the line terminal and the fixed contact of the first set of separable contacts, and the magnetic trip coil of the second trip mechanism may be electrically interconnected between the movable contact of the first set of separable contacts and the fixed contact of the second set of separable contacts.
Preferably, a first arc chute is operatively associated with a first arc runner extending from the fixed contact of the first set of separable contacts, and a second arc chute is operatively associated with a second arc runner extending from the fixed contact of the second set of separable contacts and a third arc runner which is electrically interconnected with the load terminal.